1. Field of the Invention
This invention relates generally to client-server computing architectures and communication techniques. More particularly, the invention relates to a system whereby a mobile worker and a central server may maintain a virtually continuous connection without the need to maintain a physical connection continuously.
2. Description of the Related Art
The concept of a virtual connection has arisen in connection with telecommuting and related applications. Such a system is described in U.S. Pat. No. 5,764,639. A telecommuter dials into a server using a standard telephone line. The telecommuter's modem and a modem controlled by the central server establish a connection therebetween. Once a connection is established, the telecommuter may access a computer connected to the server, read emails and receive phone calls and faxes. For example, if a customer attempts to call the telecommuter at work by dialing into a private branch exchange (PBX), the server will convert the incoming call to a packetized form, such as H.323, and redirect the call via the existing connection between the telecommuter and the server. Using this system, the telecommuter may access a computer at work, answer phone calls and answer emails. The telecommuter thus appears to be present in his or her office and thus has a virtual presence there. Note for this system to properly function, the telecommuter must stay connected to the server at all times. While this does not present a significant problem for local telecommuting, this solution is quite costly for long distance telecommuting. Likewise, this solution is very costly if the telecommuter is mobile and must maintain a virtual presence with the server using a cellular wireless connection. Furthermore, in some areas it may be difficult to maintain a wireless connection continuously. A lost connection may also prevent one from regaining access to the system until some period of time has passed. Some mobile workers require only intermittent access to the server, but find it too inconvenient to place a dial-in call and to log onto the system every time access is needed.
There is a need to provide mobile workers with various forms of virtual connectivity. Mobile workers differ from telecommuters in that while a telecommuter typically works from a single home location or remote office, a mobile worker moves from location to location during the course of a normal working day. An example of a mobile worker is a home-care professional. A home-care professional is a medical worker who periodically travels to visit with different sets of homebound patients according to their individual needs. The individual patients each have a set of medical records indicative of their medical histories. A patient's medical record is preferably maintained as an interactive electronic document containing multiple parts. For example, the medical record indicates to the home-care professional precisely what procedures are to be performed and what medications are to be administered or otherwise given to the patient. Once the services are performed, the home-care professional must annotate the medical record accordingly. The medical record is updated to reflect the patient's vital signs and other information related to patient progress. Also, a billing system takes note to track expendables and services rendered. For example, the patient may be billed per visit and each visit may involve the expenditure of billable resources such as medicines.
In the above scenario, a mobile worker must interact with a central server during the course of a day. The worker may wish to access the central server while visiting a patient. The worker may also wish to access the server from a location where only a wireless connection can be established. From a performance perspective, an ideal solution is to provide the mobile worker with a wireless connection from a remote unit to a central server. Such a wireless connection could be established via a high-powered radio connection with a broad area of coverage or via an existing cellular or personal communication system (PCS) network. Solutions using high-powered radio links have the disadvantage that costly spectrum may be required. Maintaining a link on a cellular or PCS system is expensive in that a continuous connection consumes billable airtime which is also very costly. From an airtime-cost perspective, an ideal solution would be to force the worker to create a connection, download or up load information, and work locally with data on the remote unit as often as possible. This solution is tedious, and while saving airtime costs, may actually represent the more costly solution when professional service costs are factored in. This method has the added disadvantage that when files are uploaded or downloaded the data must be synchronized in case another user has changed the data in parallel with the mobile worker. Alternatively, other users must be “locked out” of the file from the time the mobile user downloads it until it is finally uploaded with any changes made. This is the problem solved using semaphores in shared memory systems. In the context of the present invention, a “file semaphore” is a semaphore used to lock a second user out of a file while a first user is using it. Due to the aforementioned reasons, in many applications forcing the worker to repeatedly connect, disconnect, upload and download information is unacceptable.
Some mobile networks have been constructed using what is known as cellular digital packet data (CDPD). In a CDPD network, a remote unit transmits a data packet on an unused analog channel. In this sense the mobile unit remains virtually connected to a CDPD communication server. Wireless airtime is only consumed when data is actually sent. A disadvantage to this approach is CDPD networks are not universally available. Cellular coverage is much more ubiquitous than CDPD coverage. Also, CDPD network subscribers must often pay high fees and hence CDPD may not represent the most economical solution.
In some systems such as packet switched network routers, offices make use of dial-out links. Dial-out links are useful when remote offices are separated by long distances. In such systems, when a packet must be routed from a first office to a second office, a call is placed to route the packet. The dial-out connection remains connected until a no-traffic condition is detected, indicating the line is no longer active. When the no-traffic condition is detected the connection is dropped until it is again needed. Dial-out links are thus used to reduce long distance fees associated with maintaining a constant connection, and represents a useful starting point for solving the foregoing problems relating to the establishment of a virtual presence of a mobile worker. Client-server protocols and fast automated connection strategies employing dial-out links are needed to provide new ways for a mobile worker to maintain a virtual presence. Also, new methods are needed to enable dial-out links to be set up with low delays to make them more useful for novel systems.
It would be desirable to provide a system whereby a remote worker could maintain a seamless connection with a central server without the need to maintain a dedicated channel. It would be desirable if the remote worker could communicate with the central server without the need to spend time to enter a password, reconnect, and wait for a line negotiation sequence to proceed before being able to use the connection. It would be desirable for a protocol stack to activate a virtual session based on a prediction derived from a workflow. It would be desirable to use this prediction to set up a connection in the background without disturbing the mobile worker while the mobile worker performed tasks in a workflow. It would also be desirable to have a remote unit which contains most of the screen-related information needed to provide the appearance of an established connection before the connection has been fully established. It would be desirable for the remote unit to download information before it is needed and upload information after it is gathered without the user even being aware these actions are being performed. It would further be desirable to establish a virtual session using a first communication medium such as a landline and to later communicate using the same virtual session using a second communication medium such as a wireless link. This would allow a mobile worker to select the most economical or convenient means of communications at a given time. In embodiments involving modem-based connections, it would be desirable to transmit data immediately using instantly available but lower line speeds. It would be desirable to then negotiate a higher line speed in the background while the remote worker and/or the server perform other tasks. Moreover, it would be desirable to establish a session between a remote unit and a server so that various forms of communications may proceed while providing the user with the appearance the user is continuously connected to the server and has a virtual presence with the server.